おそらく・恐らくosoraku[2]nakadaka (mid-high)

1. adverbprobably; (most) likely; in all likelihood; I suspect; I dare say; I'm afraidoft. used when predicting a negative outcome
   首相しゅしょうはおそらく辞任じにんするであろう。↗

   The premier is likely to resign.

• Synonym多分たぶんNeutralMost common in speech and more casual; 「恐らく」 is slightly more formal and also common in writing. 「多分」 can also mean 'a lot, much'.
• Synonym大方おおかたNeutralAs an adverb it means 'probably, mostly', as in 「大方そんなことだろう」; it carries a conjectural tone and sounds a bit dated.
• Synonym十中八九じっちゅうはっくNeutralMeans 'in eight or nine cases out of ten'; it stresses the high probability more strongly than 「恐らく」.
• RelatedきっとNeutralMeans 'for sure, definitely', often carrying the speaker's conviction or wish; the confidence is stronger than with 「恐らく」.
• RelatedおそらくはWritten「恐らく」 with 「は」 added; the meaning is unchanged but the tone is more written and formal.
• Antonym確かにたしかにNeutralExpresses certainty ('surely, certainly'); in degree of confidence it is the opposite of 「恐らく」, which is mere conjecture.

Use 「恐らく」 for conjecture with fairly high confidence; it works in both speech and writing. For a casual guess say 「多分」. Use 「きっと」 when you are sure, and 「確かに」 to confirm a fact.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 高たかい可能性かのうせいや蓋然性がいぜんせいをもって推定すいていされることであるが。